Studies Of Secondary Relaxation Dynamics In Rigid Glass Forming Liquids

Secondary relaxations with properties closely related to the ?-relaxation have fundamental importance in glass-forming substance, and contribute to understand the condensed physics and arouse widly research for the JG-? relaxation. In this thesis the three glass-forming are studied. And this work will definitely benefit the understanding of dynamics in the glassy state.The dielectric relaxation in three glass-forming molecular liquids, 1MID, MDCP and QN are studied focusing on the secondary relaxation and its relation to the structural?-relaxation. All three glass-formers are rigid planar molecules with related chemical structures but have dipoles of different strengths at different locations. A strong and fast?-relaxation is detected in the dielectric spectra of 1MID, while no resolved ?-relaxation is observed in MDCP and QN. Apparently, the relation between f? and f? of 1MID is not in accord with the Coupling Model(CM). The possibility of the violation of the predicted relation in 1MID due to either the formation of hydrogen-bond induced clusters or the intramolecular degree of freedom is ruled out. The anomalous ?-relaxation is explained by the in-plane rotation of the dipole located on the plane of the rigid molecule contributing more intense dielectric loss at high frequencies than the JG-?-relaxation which involves out-of-plane motion. MDCP has smaller dipole moment located in the plane of the molecule, however the change of curvature of ??(f) at the high-frequency flanks reveals the JG-?-relaxation in MDCP and is in accord with the CM prediction. QN has as large an in-plane dipole moment as 1MID, and the absence of the resolved secondary relaxation is explained by the smaller coupling parameter than the latter in the framework of the CM.